Boreholes created into the earth for extraction of mineral deposits such as oil and natural gas pass through numerous and varied geologic formations. These geologic formations have varied chemical compositions, permeabilities, porosities, pore fluids, internal (pore) pressures, and material properties. Important material properties that significantly impact well construction operations include compressive strength, tensile strength, fracture initiation pressure, fracture propagation pressure, Young's (elastic) modulus, Poisson ratio and bulk modulus.
Wide contrasts in formation pressures, formation material properties, and formation fluid types often require isolation and treatment of certain geologic formations. Attempts may be made to isolate specific formations and reinforce them with steel casing, or with cement or other treatments known in the art. Where steel casings are cemented in a borehole to isolate geologic formations having significantly different properties, each of these casing strings is costly and results in a reduction in the diameter of the borehole in subsequent sections as the borehole is deepened. It is desirable, therefore, to minimize the number of casing strings required to reach the desired depth.
It is also known in the art to use cement to line boreholes, however a disadvantage of cement is that the curing step may require up to 24 hours, which is a disproportionately long period of time to wait, especially when the production site is a very costly offshore operation. A further disadvantage of cement is that in view of its particle based structure the material exhibits relatively poor penetration capability in formations, which may result in reduced sealing effect.
Various sealants are known in the art for lining or strengthening boreholes. Where sealants are employed, a resin or monomer must be selected for each well that is compatible with the drilling/completion fluid. Epoxy resins provide the best compressive strength, tensile strength and adhesion properties. However, epoxy resins and/or their curing agents generally have poor compatibility and poor performance with olefins, esters, and paraffinic hydrocarbon fluid.
Acrylate or methacrylate resins/monomers are available that are soluble in the olefin, ester, and paraffinic hydrocarbon fluids. However, alone, these monomers and resins fail to provide the type of material properties required for geosynthetic composite linings. They typically have poor tensile strength, poor fracture toughness, and low compressive strength. Blends of acrylate monomers containing prepolymers have improved tensile strength, compressive strength, and fracture toughness. However, the prepolymers used in these blends are often insoluble in the hydrocarbon fluids previously discussed.
Various methods of utilizing cements and sealants for sand consolidation are known. Sealants that have been used include, for example, a rubber based emulsion (U.S. Pat. No. 4,649,998), a rubber latex based composition (U.S. Pat. No. 5,159,980), and cement based compositions, sometimes with styrene/butadiene added (U.S. Pat. Nos. 4,721,160 and 5,258,072). Also see U.S. Pat. No. 6,177,483 which utilizes a latex based setting composition. These references typically describe the use of the described materials in sand consolidation rather than for generally strengthening the borehole to eliminate the need for a casing.
U.S. Pat. No. 5,849,674 discloses a composition comprising a clay, a polymer, a crosslinking agent, and a liquid, wherein said clay, polymer, crosslinking agent, and liquid are each present in said composition in an amount effective to form a gel.
U.S. Pat. No. 5,443,123 discloses a method of consolidating an incompetent particulate in a subterranean formation penetrated by a wellbore accomplished by introducing fluids to be injected into a wellbore into coiled tubing while the tubing is outside the wellbore and thereafter pumping the fluids from the coiled tubing into the wellbore after circulating ports open in response to initiation of a variable delay firing head for ignition of a gas generator.
Various processes for formation consolidation are disclosed, for example, in U.S. Pat. Nos. 3,536,137; 3,759,327; 4,042,032; 4,427,069; 4,669,543; 5,101,900; 5,145,013; 5,154,230; 5,178,218; and 4,936,385.
It is known in the art to use automated systems to dispense chemical treatments. Often the chemicals are mixed in large tanks that have to be cleaned and personnel are often exposed to harmful chemicals in the process of mixing and later cleaning the vessels.
There is a need in the art for a method of analyzing the material properties of exposed geological formations and determining the required changes in material properties of the exposed formation needed to continue drilling operations, while reducing or eliminating the need for setting additional casing string. In addition it would be very valuable if there were a system and apparatus available to select chemical treatment type based on material properties of the geological formation and to have the capability of automatically applying the treatment in a manner in which personnel do not have to mix harmful chemicals or clean tanks contaminated with harmful chemicals.